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25 Mil­lion Years of Us vs. Them

Like peo­ple, some of our mon­key cousins tend to take an “us ver­sus them” view of the world, a study has found. This sug­gests that the ten­den­cy for hu­man groups to clash may stem from a dis­tant ev­o­lu­tion­ary past, sci­en­tists say.

Yale Un­ivers­ity re­search­ers led by psy­chol­o­gist Lau­rie San­tos found in a se­ries of ex­pe­ri­ments that mon­keys treat mon­keys from out­side their groups with the same sus­pi­cion and dis­like as their hu­man cousins tend to treat out­siders. The find­ings are re­ported in the March is­sue of the Jour­nal of Per­son­al­ity and So­cial Psy­chol­o­gy.

“One of the more trou­bling as­pects of hu­man na­ture is that we eval­u­ate peo­ple dif­fer­ently de­pend­ing on wheth­er they’re a mem­ber of our ‘in­group’ or ‘out­group,’” San­tos said. “Pretty much eve­ry con­flict in hu­man his­to­ry has in­volved peo­ple mak­ing dis­tinc­tions on the ba­sis of who is a mem­ber of their own race, re­li­gion, so­cial class, and so on. The ques­tion we were in­ter­est­ed in is: Where do these types of group dis­tinc­tions come from?”

The an­swer, she adds, is that such bi­ases have ap­par­ently been shaped by 25 mil­lion years of ev­o­lu­tion and not just by hu­man cul­ture.

“The bad news is that the ten­den­cy to dis­like out­group mem­bers ap­pears to be ev­o­lu­tion­arily quite old, and there­fore may be less sim­ple to elim­i­nate than we’d like to think,” San­tos said. “The good news, though, is that even mon­keys seem to be flex­i­ble about who counts as a group mem­ber. If we hu­mans can find ways to har­ness this evolved flex­i­bil­ity, it might al­low us to be­come an even more tol­er­ant species.”

San­tos and mem­bers of her lab stud­ied rhe­sus ma­caque mon­keys liv­ing on an is­land off the coast of Puerto Rico. Mon­keys in this popula­t­ion nat­u­rally form dif­fer­ent so­cial groups based on family his­to­ry.

The in­ves­ti­ga­tors ex­ploited a well-known ten­den­cy of an­i­mals to stare long­er at new or fright­en­ing things than at fa­mil­iar or friendly things. They showed mon­keys pic­tures of oth­er mon­keys who were ei­ther in their so­cial group or mem­bers of a dif­fer­ent group. They found that mon­keys stared long­er at pic­tures of oth­er mon­keys who were out­side their group, sug­gest­ing the crea­tures spon­ta­ne­ously de­tect who is a strang­er and who is a group mem­ber.

* * *

The Yale team’s re­sults sug­gest that the dis­tinc­tions hu­mans make be­tween “us” and “them”— and there­fore the roots of hu­man prej­u­dice—may date back at least 25 mil­lion years, when hu­mans and rhe­sus ma­caques shared a com­mon an­ces­tor.

“So­cial psy­chol­o­gists in­tro­duced the world to the idea that the im­me­di­ate situa­t­ion is hugely pow­er­ful in de­ter­min­ing be­hav­ior, even in­ter­group feel­ings,” said [Situationist Contributor] Mahza­rin Ba­naji of Har­vard Un­ivers­ity, a co-author of the pa­per. “Evo­lu­tion­ary the­o­rists have made us aware of our an­ces­tral past. In this work, we weave the two to­geth­er to show the im­por­tance of both of these in­flu­ences at work.”

2 Responses to “25 Mil­lion Years of Us vs. Them”

[…] The evolutionary psych story about humanity is that war, genocide, and the divisive “-isms” that keep humans in a perpetual state of conflict are inevitable expressions of an “us vs. them” tendency that is simply a part of our biological makeup. […]

[…] The evolutionary psych story about humanity is that war, genocide, and the divisive “-isms” that keep humans in a perpetual state of conflict are inevitable expressions of an “us vs. them” tendency that is simply a part of our biological makeup. […]